On 2002-06-24 18:00, "ext Jonathan Borden" <jonathan@openhealth.org> wrote:
> Patrick Stickler wrote:
>
>>
>> On 2002-06-24 10:47, "ext Patrick Stickler" <patrick.stickler@nokia.com>
>> wrote:
>>
>>>
>>> On 2002-06-21 15:53, "ext Jonathan Borden" <jonathan@openhealth.org>
> wrote:
>>>
>>>> The concept of "dark triples" as a layering option seems to be getting
> a bit
>>>> misunderstood. The essence of "dark" or "unasserted" triples is simply
> that,
>>>> from a technical perspective, it is difficult (some would indeed say
>>>> impossible) to define a language such as OWL (and given the constraints
>>>> placed on this language by the WebOnt charter etc.) in RDF if OWL is to
> have
>>>> the characteristics we desire, and RDF triples are all "truths".
>>>
>>> I consider RDF to already have a mechanism for expressing unasserted
>>> triples, namely reification. The only reason folks want to create
> something
>>> else, IMO, is simply because the RDF/XML syntax is so obese. I.e.
>>>
>>> <rdf:Statement>
>>> <rdf:subject rdf:resource="#foo"/>
>>> <rdf:predicate rdf:resource="&owl;bar"/>
>>> <rdf:object rdf:resource="#bas"/>
>>> </rdf:Statement>
>
> Yes, this syntax is not acceptable for Semantic Web languages that are are
> to be 'layered' on RDF.
>
> ...
>> Note also that unasserted "dark" statements at the RDF-level can be
>> asserted at any given higher level where they have meaning in a automated
>> and generic fashion.
>>
>> OWL level assertions can be easily automated using this approach
>> by a single rule:
>>
>> {
>> ?x rdf:type rdf:Statement .
>> ?x rdf:subject ?s .
>> ?x rdf:predicate ?p .
>> ?x rdf:object ?o .
>> ?p rdf:type owl:OWLPredicate .
>> }
>> log:implies
>> {
>> ?s ?p ?o .
>> }
>>
>> Done.
>>
>
> Well these sorts of issues and purported solutions appear to be a uniform
> characteristic of attempts to develop languages _in_ RDF that are also to be
> layered _on_ RDF (e.g. TimBL's "layer cake" as it is called).
>
> Don't you see what you are trying to do?
>
> You are writing an N3 formula _which is not RDF but as if it were something
> in RDF_ and casually tossing this out as a solution to some problem _in
> OWL_.
>
> How is OWL to use such a formula if OWL is to be layered on RDF? How are
> such rules supposed to be specified? Sure if we accept N3 this is no problem
> but that's the point: N3 formulas, when represented as triples, use
> collections of unasserted triples. This is most basic:
>
> X=> Y
>
> does not imply (i.e. assert) X so you need a way to _say_ "X" without
> asserting X.
>
> But hold on and understand this:
>
> You are proposing RDF reification as a way to 'implement' unasserted triples
> but you are using _another_ mechanism of unasserted triples in order to
> 'implement' reification. It is exactly these sorts of arguments that are
> akin to trying to develop a perpetual motion machine.
>
> So certainly if you give us a mechanism for N3 formulae the problem would be
> solved. That is the whole point, really.
>
> Jonathan
As I mentioned in another posting, how a given upper layer asserts
the statements that are meaningful at the upper layer which are
unnasserted at the lower layers is not central to the approach
I was proposing.
I was using N3 simply to illustrate that it can be easily automated.
It can be simply a requirement on all OWL processors that they "pretend"
that unasserted RDF statements which contain OWL predicates are
asserted -- or part of an OWL preprocessor on an RDF graph which
maps unasserted OWL statements into asserted RDF statements. Whatever.
The point is that OWL statements are unasserted at the RDF layer
and applications at the lower layers need not concern themselves
with special "reserved vocabularies" of upper layers and "pretend"
that asserted statements using such vocabularies are not in fact
asserted.
--
Patrick Stickler Phone: +358 50 483 9453
Senior Research Scientist Fax: +358 7180 35409
Nokia Research Center Email: patrick.stickler@nokia.com